Aluminum (Al) is ubiquitous in soils and at pH values below 5.0, is solubilized into the soil solution as the highly phytotoxic Al3 species, which inhibits root growth and damages root systems (Kochian, 1995, Annu. Rev. Plant Biol. 46: 237-260). As such, aluminum toxicity is aggravated by acid precipitation (e.g., acid rain). For example, contaminated soils in Brazil contain aluminum in amounts that range from 11 to 124 g/Kg of soil. Another constraint on acid soils is phosphorous (P) deficiency, which is caused by P fixation with Al and Fe oxides on the surface of clay minerals in acid soils. See Sanchez et al. 1997. In: Replenishing Soil Fertility in Africa, ed. R Buresh, P Sanchez, F Calhoun, pp. 1-46). Root damage reduces water and nutrient uptake and thus crop productivity. Low soil pH has been documented to reduce the yield on nearly 25% of the world's land presently under production. See, Wood, et al. (2000) in Pilot Analysis of Global Ecosystems: Agroecosystems (Int. Food Policy Res, Inst. And World Resources Inst., Washington, D.C.), pp 45-54). Thus, there is a need to provide methods and materials for increasing aluminum tolerance in plants.